1. Field of the Invention
The present invention relates to pressurized hydraulic fluid systems in general and, more particularly, to a pressurized hydraulic fluid system including a main pump and a charge pump provided for maintaining a sufficient inlet head pressure in the main pump under all conditions.
2. Description of the Prior Art
Conventionally, pressurized hydraulic fluid systems of the prior art include a main hydraulic unit, such a pump or motor/pump, provided for various applications, such as driving hydraulic motors or actuators, or charging high-pressure hydraulic accumulators. Usually, the hydraulic pumps, particularly, but not limited to, high performance piston pumps, require a positive head pressure on an inlet (suction) side thereof on some operating conditions. Examples of such operating conditions include, however are not limited to, high-speed operations, when a high viscosity hydraulic fluid is employed, or cold weather operation. In many such applications a dedicated charge pump is used between a fluid reservoir and the high performance hydraulic pump to create and maintain the positive head pressure on the inlet side thereof. Typically, the charge pump is driven by a power source separate from the main pump and a prime mover driving the main, high performance hydraulic pump. Such an arrangement of the pressurized hydraulic fluid system presents many disadvantages including the fact that the charge pumps of the prior art having separate power source cannot compensate for variations in flow rates passing through the high performance hydraulic pumps. Moreover, in many applications, it is not possible to mount the power source in proximity to the reservoir mounted charge pump.
Accordingly, it is the intent of this invention to overcome these shortcomings of the prior art by allowing for a portion of the hydraulic power converted from the power source to be used to drive the “remote” charge pump.